The term "tubular membrane module" is used to refer to a component which includes a series of permeable membranes of tubular configuration each supported on the inner surface of a porous pipe such as a glass fibre-reinforced fabric pipe. The pipes are enclosed within an outer housing having a permeate outlet. Fluid to be treated is passed through the pipes under pressure. Permeate passes through the membranes and pipes into the interior of the outer housing and leaves through the permeate outlet.